In the technical trend toward higher-density magnetic disks (also called hard disks), so-called bit-patterned media that have magnetic-recording magnetic dots segmented by nonmagnetic portions have been suggested to reduce degradation of magnetic signals due to thermal fluctuations. According to a suggested method of manufacturing a bit-patterned medium, dots are formed by utilizing the self-assembling capability of a block copolymer, and magnetic dot patterns are obtained by processing the dots. However, controlling dots to be arranged in a perfect array over a wide area is considered particularly difficult. In view of this, there is a technique to control the array by using guide patterns formed with walls or cylindrical portions or the like.
A magnetic disk includes servo region patterns for controlling recording and reproduction, and data region patterns for recording and reproducing data. Normally, different patterns are used as those patterns.
In a case where a self-assembled material is used in the manufacture of a magnetic disk, respective bit patterns are first formed by applying a diblock copolymer solution having a self-assembling capability to the insides of guide patterns that are formed on the substrate surface beforehand through an electron beam lithography process, an imprint process, or a process performed after the electron beam lithography process or the imprint process. An annealing process is then performed to cause microlayer separation into a first component aggregated in dots and a second component coating the dots. After that, the respective dots are self-assembled and are ideally arranged in a hexagonal array. By utilizing the difference in etching characteristics (the etching rate difference) between the first component and the second component, the substrate is processed with the first component or the second component serving as a mask. In this manner, bit patterns can be formed. At this point, the servo regions preferably have servo patterns already formed through the electron beam lithography process, the imprint process, or a process performed after the lithography process or the imprint process. This is because, with the servo patterns already formed, the procedure for magnetically forming the servo patterns with a magnetic head (hereinafter referred to as the servo track write) can be advantageously skipped, and there is no difference between the eccentricity of the disk and the eccentricity at the time of the servo track write. Such a difference causes a problem in cases where the servo track write is performed.
In a case where a self-assembled material is used in the manufacture of a magnetic disk as described above, servo patterns can be formed beforehand in the servo regions through an electron beam lithography process, an imprint process, or a later process.
In general, a servo pattern is a pattern that extends in a radial direction perpendicular to the data track direction, and the boundary between a servo region and a data region is also a pattern that extends in a radial direction. In a hard disk drive, magnetic signal reading and writing are performed with a magnetic head to which an arm operating to draw arc-like trajectories is attached. Therefore, to shorten the seek time, the servo region patterns are preferably formed in arc-like shapes conforming to the arm trajectories.
Meanwhile, the self-assembling capability of a self-assembled material that is tended to become a hexagonal close-packed structure is utilized in the data regions. Therefore, if the boundary between a servo region and a data region is a straight structure with uniform thickness, the distance between the boundary and a post pattern for controlling the array of the self-assembled material dots cannot be kept at a constant value. As a result, the control on the array of the self-assembled material dots cannot be appropriately performed at the boundary portion. Further, if the boundary between a servo region and a data region has an angle that varies with the arm's trajectories, the control on the array at the time of self-assembling is degraded. As a result, synchronous data reading and writing might not be performed in the defective array region.